The embodiments described herein relate generally to the field of non-destructive evaluation (NDE). Infrared flash (or pulsed) thermography is an example of a technique for NDE used primarily in the inspection of thin nonmetallic materials, such as laminated or bonded composites in the aerospace industry. IR flash thermography is primarily used to detect delamination-like anomalies, although surface cracks may also be detected to some extent. In one embodiment, a single-sided or reflection technique is used wherein the flash lamp (heat source) and the IR camera (detector) are on the same side of the test object undergoing inspection.
The hardware equipment for an IR flash thermography system comprises a flash lamp (source of light/heat), a flash hood, a flash power supply/trigger unit, a flash duration controller, an IR camera for capturing video images, data acquisition electronics, and a computer. The computer is used for controlling the flash trigger, for acquiring video data from the IR camera, for displaying data, and for post-processing of the acquired data.
In one example of an NDE technique using IR flash thermography, a plate is provided as a test object with a round delamination in the center. After applying heat to the top surface of the test object by triggering the flash lamp, the top surface area surrounding the anomaly cools faster than the top surface (footprint) area above the anomaly. The IR camera captures a sequence of images of the surface temperature in terms of pixel intensity and shows the anomaly as a hot spot (e.g., an area warmer than the surrounding area or the reference region of interest (ROI)). The hot spot is about the size and shape of the anomaly footprint. Relative pixel intensity, i.e., the difference in pixel intensity between the hot spot (measurement ROI) and surrounding area (reference ROI), varies with the post-flash time. Deeper anomalies appear at later times in the IR video data compared to the near surface anomalies. After the appearance of an anomaly in the IR video data, the relative pixel intensity continues to increase with time. The relative pixel intensity of the anomaly reaches a peak at a certain time and then the relative pixel intensity decays until the temperature of the indication area and the temperature of the surrounding area become equal.